Different Ways Of Taking Food

As established in Chapter 1, animals cannot make their own food and rely on plants (directly or indirectly) for nutrition. Food provides the necessary **nutrients** for an animal's growth, tissue repair, and overall bodily functions.

Food contains complex substances like carbohydrates, proteins, and fats. Before these can be used by the body, they must be broken down into simpler forms. The process of converting **complex food components into simpler substances** is called **Digestion**.

---

Organisms have developed diverse strategies for taking food into their bodies, referred to as their **mode of feeding**.

Some examples of feeding modes observed in different animals include:

• **Sucking:** Bees and hummingbirds suck nectar from flowers; human infants and young animals feed on mother's milk.
• **Swallowing:** Snakes like pythons swallow their prey whole.
• **Filtering:** Some aquatic animals filter tiny food particles present in the water around them.
• Other modes include Scraping, Chewing, Siphoning, Capturing, Sponging, etc.

---

Activity 2.1

This activity involves observing various animals to identify the type of food they eat and their specific mode of feeding, illustrating the diversity of feeding strategies in the animal kingdom.

Table 2.1: Various modes of feeding (Examples):

Name of animal	Kind of food	Mode of feeding
Snail	Algae, plants	Scraping
Ant	Insects, sugar, food particles	Chewing, Swallowing
Eagle	Other animals (meat)	Capturing and swallowing/tearing
Humming-bird	Flower nectar	Sucking
Lice	Blood	Sucking
Mosquito	Blood	Sucking (piercing and sucking)
Butterfly	Flower nectar	Siphoning (using a tube-like proboscis)
House fly	Decaying matter, sweet substances	Sponging (lapping up liquid food)

---

Amazing Fact about Starfish Digestion:

Starfish exhibit a remarkable digestive process. They feed on animals enclosed within hard shells, like clams. After opening the shell, the starfish actually extends its **stomach** out through its mouth and into the shell to digest the soft body of the prey externally. Once digestion is partially complete, the stomach is withdrawn back into the starfish's body, where digestion continues.

Digestion In Humans

In humans, food is taken into the body through the mouth, undergoes digestion and absorption, and the unused waste is eliminated. The process of digestion in humans is complex and involves a system of organs.

The human digestive system consists of a long, continuous tube called the **alimentary canal** (also known as the digestive tract) and several associated glands that secrete digestive juices.

The alimentary canal starts at the **buccal cavity** (mouth) and ends at the **anus**. It is divided into various compartments in sequence:

1. Buccal cavity (Mouth)
2. Foodpipe (Oesophagus)
3. Stomach
4. Small intestine
5. Large intestine (ending in the Rectum)
6. Anus

As food travels through these compartments, it is gradually digested. The digestive juices secreted by the inner walls of the stomach and small intestine, as well as by major digestive glands (salivary glands, liver, pancreas), help break down complex food substances into simpler ones that the body can absorb and utilise.

---

The Mouth and Buccal Cavity:

The process of taking food into the body is called **Ingestion**. In humans, ingestion happens through the mouth (buccal cavity). Inside the mouth, food is mechanically broken down by the **teeth** through chewing. Teeth are rooted in sockets within the gums and come in different shapes and sizes, performing different functions based on their structure.

Types of teeth in adults (usually 32 in total - 16 in each jaw):

• Incisors: For cutting and biting (8 total, 4 in each jaw).
• Canines: For piercing and tearing (4 total, 2 in each jaw).
• Premolars: For chewing and grinding (8 total, 4 in each jaw).
• Molars: For chewing and grinding (12 total, 6 in each jaw).

---

Activity 2.2

This activity involves examining one's own teeth in a mirror to identify and count the different types of teeth (incisors, canines, premolars, molars) and understand their functions (cutting, tearing, chewing) by observing which teeth are used for eating different types of food like apple or bread.

Table 2.2: Recording observations about teeth:

Type of teeth	Number of teeth	Total
Cutting and biting teeth (Incisors)	... Lower jaw, ... Upper jaw	...
Piercing and tearing teeth (Canines)	... Lower jaw, ... Upper jaw	...
Chewing and grinding teeth (Premolars and Molars)	... Lower jaw, ... Upper jaw	...

---

Milk Teeth and Permanent Teeth:

Humans have two sets of teeth during their lifetime. The first set, called **milk teeth** (or deciduous teeth), grows during infancy and typically falls out between the ages of six and eight years. These are replaced by a second set, called **permanent teeth**, which are expected to last throughout life, though they can be lost in old age or due to disease.

---

The mouth also contains **salivary glands** that secrete **saliva**. Saliva plays a role in the chemical digestion of food, particularly carbohydrates.

---

Activity 2.3

This activity demonstrates the action of saliva on starch. Two test tubes are prepared: one with boiled rice and water, and the other with rice chewed for a few minutes mixed with water. Iodine solution is added to both. The test tube with plain boiled rice and water will turn blue-black (indicating starch presence), while the test tube with chewed rice and water will show less or no blue-black colour. This is because the saliva in the chewed rice breaks down some of the starch into simpler sugars, which do not give a blue-black colour with iodine. This shows that **saliva digests starch into sugars**.

---

The **tongue** is a muscular organ in the mouth that helps in talking, mixing saliva with food during chewing, and swallowing. The tongue also has **taste buds** on its surface that allow us to detect different tastes (sweet, salty, sour, bitter) in food.

---

Activity 2.4

This activity maps the approximate locations of taste buds sensitive to different tastes on the tongue. By applying solutions of different tastes (sweet, salty, sour, bitter) to various areas of a classmate's tongue while they are blindfolded, one can determine which regions are more sensitive to each taste.

---

Foodpipe (Oesophagus):

After being chewed and mixed with saliva in the mouth, the food is swallowed and passes into the **foodpipe** or **oesophagus**. The oesophagus is a tube that runs down the neck and chest, connecting the mouth to the stomach.

Food is pushed down through the oesophagus by a wave-like muscular movement of its walls, a process called **peristalsis**. This movement continues throughout the alimentary canal to move food along.

Sometimes, the stomach rejects food (e.g., due to indigestion or illness), leading to food being pushed back up and expelled through the mouth. This is called **vomiting**.

Note: The throat has a common passage for both air (windpipe) and food (foodpipe). A flap-like valve automatically covers the opening of the windpipe during swallowing to ensure food enters only the foodpipe, preventing choking.

---

The Stomach:

The **stomach** is a thick-walled, J-shaped bag that is the widest part of the alimentary canal. It receives food from the oesophagus and passes it into the small intestine.

The stomach's inner lining secretes:

• **Mucus:** Protects the stomach lining from its own secretions.
• **Hydrochloric acid:** Creates an acidic environment that kills harmful bacteria entering with food and helps digestive juices work effectively.
• **Digestive juices:** Begin the digestion of **proteins**, breaking them down into simpler substances.

The stomach also churns the food, mixing it with these secretions.

Amazing Fact about Stomach Function:

The functioning of the stomach was notably studied through a medical case in 1822 involving Alexis St. Martin, who had a permanent opening in his stomach due to a gunshot wound. Dr. William Beaumont observed the stomach churning food, secreting digestive fluid, and emptying into the intestine only after digestion was completed.

---

The Small Intestine:

The **small intestine** is a long (about 7.5 meters in length) and highly coiled tube. It is the primary site for complete digestion and absorption of food.

It receives digestive juices from two major glands:

• Liver: The largest gland in the body, located in the upper right abdomen. It secretes **bile juice**, which is stored in the **gall bladder**. Bile is crucial for the digestion of **fats**.
• Pancreas: A cream-coloured gland located below the stomach. It secretes **pancreatic juice**, which acts on **carbohydrates, fats, and proteins**, converting them into simpler forms.

The wall of the small intestine also secretes its own digestive juice (**intestinal juice**), which completes the digestion process.

By the time food reaches the lower part of the small intestine, all food components are broken down:

• Carbohydrates into simple sugars like **glucose**.
• Fats into **fatty acids** and **glycerol**.
• Proteins into **amino acids**.

---

Absorption in the Small Intestine:

The digested food, now in simpler forms, passes through the wall of the small intestine into the **blood vessels**. This process is called **Absorption**.

The inner walls of the small intestine have thousands of tiny, finger-like projections called **villi** (singular: villus). Villi significantly **increase the surface area** available for the absorption of digested food. Each villus contains a network of blood vessels close to its surface, into which the absorbed nutrients pass.

The absorbed substances are then transported by the blood to various organs of the body. Here, they are used to build complex substances needed by the body, such as proteins. This process is called **Assimilation**.

In cells, glucose (simple sugar from carbohydrate digestion) is broken down using oxygen to release **energy**, along with carbon dioxide and water.

---

Large Intestine:

The food that is not digested or absorbed in the small intestine enters the **large intestine**. The large intestine is wider and shorter than the small intestine, measuring about 1.5 meters in length.

Its main function is to absorb **water and some salts** from the remaining undigested food material. This process converts the liquid waste into semi-solid faeces.

---

Rectum and Anus:

The remaining waste material, now in semi-solid form (faeces), passes into the **rectum** and is stored there temporarily. The faecal matter is then removed from the body through the **anus** periodically. This process of elimination of undigested waste is called **Egestion**.

---

Diarrhoea:

Diarrhoea is a condition characterized by frequent passing of watery stools. It can be caused by infection, food poisoning, or indigestion. Diarrhoea leads to excessive loss of water and salts from the body and can be dangerous, especially for children. It is crucial to stay hydrated by drinking plenty of boiled and cooled water with dissolved salt and sugar (Oral Rehydration Solution - ORS) and seek medical advice if needed.

Digestion In Grass-Eating Animals

Grass-eating animals like cows, buffaloes, and deer are called **Ruminants**. They have a unique digestive system adapted to digest cellulose, a complex carbohydrate abundant in grass, which most other animals (including humans) cannot digest efficiently.

Ruminants quickly swallow large amounts of grass and store it in a special part of their stomach called the **rumen**. In the rumen, food is partially digested by specific bacteria present there. This partially digested food is called **cud**.

Later, when the animal is resting, the cud is brought back into the mouth in small lumps, and the animal chews it thoroughly. This process is called **Rumination**. Chewing the cud helps break down the grass further physically.

The bacteria in the rumen are capable of digesting **cellulose**. This process breaks down the cellulose in the grass, making its nutrients available to the ruminant. Humans lack these specific cellulose-digesting bacteria in sufficient quantities, which is why we cannot digest grass or hay effectively.

Some animals like horses and rabbits have a large sac-like structure called the **caecum** between the oesophagus and small intestine. Digestion of cellulose in these animals occurs in the caecum with the help of certain bacteria.

Feeding And Digestion In Amoeba

**Amoeba** is a single-celled, microscopic organism found in pond water. It is a simple organism without a mouth or a complex digestive system like in humans.

Amoeba has a cell membrane, a nucleus, and small bubble-like vacuoles in its cytoplasm. Amoeba constantly changes its shape and moves using temporary, finger-like projections called **pseudopodia** ("false feet"). Pseudopodia are also used for capturing food.

Amoeba feeds on microscopic organisms. When it senses food, it extends its pseudopodia around the food particle and engulfs it. The food particle becomes trapped inside a small sac-like structure within the Amoeba called a **food vacuole**.

**Digestion** in Amoeba occurs within the food vacuole. Digestive juices are secreted into the food vacuole, breaking down the complex food into simpler substances. These simpler substances are then **absorbed** into the cytoplasm and used for the Amoeba's growth, maintenance, and multiplication.

The undigested waste material remaining in the food vacuole is expelled outside the cell by the vacuole, a form of **egestion**.

Although the mechanisms are different, the basic process of obtaining nutrients, digesting food, absorbing nutrients, and releasing energy is similar in all animals, from simple single-celled organisms like Amoeba to complex multicellular organisms like humans.

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer:

Answer: